The Tiber is a natural barrier across the land route which runs up and down the west coast of central Italy. The first place upstream at which it can be bridged is about 15 miles (24 km) from the coast, where an island in the river is overlooked by several steep hills rising above the marshy plain. Boats can make their way this far up the river, but marauding pirates will not risk venturing into such a likely trap.

This is an obvious place for a prosperous settlement. It is the site of Rome.

There is evidence of Bronze Age settlement on the various hills of Rome. By the 8th century BC local villages are combining into something more like a town. The centre of their community is the low-lying ground between the Capitoline and Palatine hills, an area later known as the Forum. Drained and paved in the 7th century BC, it becomes and will remain the centre of Roman government.

By about the end of the 7th century the rulers of Rome are kings from a more developed civilization to the north, that of the Etruscans.

Etruscan rule in Rome is brought to a sudden end late in the 6th century. Roman legend provides a dramatic story to account for a rebellion by the Roman people.

The Etruscan king, Tarquin the Proud, has a son, Sextus Tarquinius, who rapes a Roman lady of exceptional virtue, Lucretia. She makes public the crime and then stabs herself. The outrage provokes a public uprising, led by Brutus. The Etruscans are driven from Rome.

The rape of Lucretia later becomes a favourite subject in art, as do other stories about the Etruscans and Rome. One concerns the two sons of Brutus, who conspire to restore the Tarquin dynasty. Brutus himself condemns them to death, putting the interests of the new republic above family ties.

Another dramatic legend embroiders the historical attempt of an Etruscan king, Lars Porsena of Clusium, to recover Rome. A brave soldier, Horatius Cocles, holds off the Etruscan army single-handed on the bank of the Tiber while other Romans, behind him, demolish the wooden bridge which leads across the river to the city.

Senators, consuls and tribunes: from 509 BC

The traditional date for the ending of Etruscan rule and the founding of the Roman republic is 510 BC. This is probably not far from the truth.

The Roman senate, already in existence as an advisory body to the Etruscan kings, now chooses two officials from among its own number to become joint heads of state. Known at first as praetors, and later as consuls, they are elected only for a year. Each has a veto on any action of the other. To avoid stalemate in a crisis, the constitution of the republic provides for another more powerful office. An overall leader may be appointed, with the title of dictator, for a period not exceeding six months.

The senate consists of 300 members whose appointment is for life. The senators select the men who are to fill the vacancies in their number caused by death, and they recommend each year which two from among themselves shall be consuls. The system is perfectly designed for a small number of aristocratic families to hold on to power.

The result is that the vast majority of the Roman people (the plebs) soon feel excluded from the benefits of the new republic. As early as 494 the plebs organize a concerted protest. They withdraw from all civic activities.

The patrician senators give in to pressure from the plebs for a good reason. Rome's army, on which the city's success and survival depends, is at this stage a citizen army. All citizens are liable for service, and the vast majority are from the plebs. A mass refusal to comply is a persuasive argument. The 494 protest has no need to be other than peaceful.

The result is the creation of two powerful new officials, the tribunes of the people. They are to be elected annually and their task will be to safeguard plebeian rights. By 449 BC there are as many as ten tribunes. They remain important officials, though their radical function becomes blunted when a plebeian elite begins to emerge.

Over the years a few plebeian families grow in wealth and prestige through being frequently elected to high office. From 367 BC one of the two consuls each year is from the plebs. A plebeian aristocracy develops, closer to the patrician class than to the people.

The real distinction now is between the owners of land and the poor of the towns. The urban poor, together with freed slaves, are classed as proletarians. Their numbers grow, as the use of slaves on large country estates forces smallholders to sell up and seek work in the city. Soldiers are now paid (from early in the 4th century), but proletarians are not even allowed to serve in the legions which are steadily extending Rome's frontiers.

The Roman legions: from the 4th century BC

In the early years of Rome's history Roman soldiers form up for battle in a Greek phalanx, but by the 4th century a distinctive tactic is beginning to emerge in the deployment of the Roman legion.

The essence of the change is the division of the army into companies of 120 men, known as maniples. Each maniple is formed up on the battle ground as a block 12 abreast and 10 deep. Instead of the serried ranks of the Greek phalanx, the soldiers stand about 5 feet apart within each maniple; and the maniples are deployed on the field like three rows of squares on a chessboard (each black square a block of men, each white square open space).

In the first shock of battle each maniple knows that there is a space behind into which it can fall back. By the same token a maniple of the second or third rank has space in front, where it can move to give support. And enemy forces may be enticed into a space between maniples, where they can be attacked from both sides. This is very different from the rigid once-for-all clash of two solid phalanxes.

In keeping with this more open role, the weapons of the Roman foot soldier are gradually modified.

Arms of the Roman legionary: from the 4th century BC

In a Roman army the long heavy spear of the Greek hoplite is replaced by a javelin. The Roman foot soldier flings this as soon as he is in close contact with the enemy. He then gets to work with his short thrusting sword, the most characteristic weapon of the Roman legionary.

The Roman helmet is simpler than the Greek version, with more of the face exposed. And the Roman shield is rectangular, with a slight curve so that it hugs the body. Held edge to edge above the head, these shields can form a roof to protect soldiers carrying out a siege - the famous Roman testudo or 'tortoise'.

Roman expansion in Italy: 5th - 4th century BC

Rome's military skill is a crucial element in the growth of her empire, but the start is decidedly slow. Her nearest rival is the Etruscan town of Veii, a mere 10 miles (16 km) to the northwest. Rome throws off the rule of the Etruscans in about 509, yet it takes more than a century of skirmishes between these two very close neighbours before Rome finally captures Veii in 396 BC.

The insecurity of Rome herself is dramatically demonstrated a few years later. The Romans find themselves helpless against Celtic tribesmen, marauding south through Italy in search of booty. In about 390 the Celts enter Rome and burn much of the city before departing north again.

From this low point in the early 4th century, the expansion of Roman power progresses more smoothly. An important element in this success is political. Victories on the battlefield are reinforced by settlements which give the defeated towns an involvement in the success of Rome.

The closeness of that involvement varies. Some of the nearby communities to the south, sharing the Latin language with the Romans, are granted full Roman citizenship. Other Latins have only a limited form of citizenship. More distant communities, of differing languages and cultures, are given the status of allies. They must supply troops or ships to support Rome, but they are left in charge of their own affairs.

Rome reinforces this network of alliances with a sound system of communication. In 312 the first of the great Roman roads, the Via Appia, is built by Appius Claudius to link Rome with an important new ally - the city of Capua, north of Naples.

Additional security is provided by small colonies planted at strategic places. In each of them 300 Roman families are settled in a walled encampment, becoming in effect a self-sufficient military outpost. Each family is given its own plot of land; the men are of an age to be liable for military conscription if still in Rome. One of the first colonies is established in about 400 BC at Ostia, defending the mouth of the Tiber.

Enemies overseas: 3rd - 2nd century BC

Early in the 3rd century Roman pressure begins to be felt as far south as the heel of Italy, where Tarentum is one of the oldest Greek colonies. The inhabitants appeal for help to an ambitious ruler, Pyrrhus, who has been vigorously extending his kingdom of Epirus on the other side of the Adriatic.

Pyrrhus sails in 281 BC with some 25,000 men and 20 elephants, the first to be seen in Italy. During the next two years he defeats the Romans in three battles, with heavy casualties on both sides. When he finally returns to Epirus, in 275, he has only a third of his original force - having achieved, in the phrase through which his name lives, nothing but Pyrrhic victories. He leaves a garrison in Tarentum, but the city falls to Rome in 272.

Pyrrhus has been the Romans' first adversary from overseas. Their dismissal of him, and their subsequent capture of the Greek city of Tarentum, sends a clear message to the Mediterranean world. There is a major new power in the west.

The two dominant colonial groups of the region are the Greeks and the Phoenicians, or Carthaginians. Both have well-established colonies close to the shores of Italy.

The natural flashpoint between the three powers is the nearest overseas territory to mainland Italy, the island of Sicily, exceptionally fertile and later known as the 'bread basket of Rome'. Its eastern section is a Greek colony, while its western parts are Carthaginian.

The Romans intervene on the Greek side in a dispute, sparking off in 264 the first of three wars with the Carthaginians, known as the Punic Wars. The final score, three-nil, demonstrates the power of the upstart.

In the first Punic War (264-241) Rome wins the whole of Sicily, which becomes the first overseas province of the Roman empire. In the second (218-201) the Carthaginians are driven out of Spain, in spite of a dramatic achievement during the conflict - Hannibal's crossing of the Alps and invasion of Italy.

The third war (149-146) ends with the Romans destroying the city of Carthage and selling into slavery the surviving Carthaginians.

The province of Sicily: 241 BC

Sicily is a valuable new possession for Rome in 241, and its acquisition prompts a new arrangement. Territories in mainland Italy, given the status of allies, must provide men for Roman armies. But the manpower of Sicily is less interesting to Rome than its agricultural wealth. Moreover both Carthagians and Greeks have developed an excellent means of exploiting the native Sicilians. A proportion of their produce is demanded as tax.

Rome, adopting this system, finds that a governor, with a supporting army, is necessary to ensure that the funds are collected. Sicily becomes Rome's first province - the adminstrative unit by means of which an empire will develop. Sardinia and Corsica are added, in 227, as the second Roman province.

Campaigns east and north: 2nd - 1st century BC

By 200 BC the western Mediterranean is effectively under Roman control, but the east is still under the influence of Greece - part of the empire created more than a century earlier by Alexander the Great. Descendants of his generals are now independent kings in Alexander's original homeland of Macedonia, in Syria and in Egypt.

The rulers of these empires are in almost constant conflict with each other and with their neighbours over territory in the eastern Mediterranean. Rome becomes involved when independent Greek states in the Aegean appeal for help against aggression from Macedonia.

A Roman expedition defeats the Macedonians in 197. The Roman commander then uses an occasion when representatives of all the Greek communities are gathered together, at the Isthmian games in 196, to make a dramatic announcement: all Greek states are now free, under Roman protection.

It means less than it might, for in 194 the Roman army returns home to Italy - leaving the Greeks to enjoy their freedom. This they do in their usual manner, with a rapid return to armed conflict. The Romans intervene on several occasions, apparently with reluctance. But by 148 their patience is at an end. Macedonia is annexed as a Roman province. From it a loose control is exercised over the rest of mainland Greece and the Aegean.

Roman territories are also being greatly extended in the north of the Italian peninsula, pressing back the Celtic tribes who have settled in the Po valley. A colony is established at Rimini in 268; by 220 the Via Flaminia links it with the capital. Bologna becomes a colony in 189, followed by Parma and Modena in 183.

Subsequent Roman campaigns bring territory under control as far north as the Alps and westwards along the coast. The south of France is made a Roman province in 121 BC, as Transalpine Gaul. Northern Italy becomes in 81 the province of Cisalpine Gaul.